From the Custom Start & End Times menu (Admin Control Panel -> Settings -> Listing Settings -> Global Settings -> Custom Start & End Times):

Enable Custom Start Time

If checked, enables the custom start time option for listings.

Enable Custom End Time

If checked, enables the custom end time option for listings.

Note: If not enabled, only the listing duration selector will be available.

From the Create Listing (Listing Settings section) menu, select:

Custom Start Time

and

End Time